fix: add extensive logging and fix subprocess PIPE blocking

1. CI Logging Enhancements:
   - Added comprehensive diagnostics with process tree, network listeners, file descriptors
   - Added timestamps at every stage (before/during/after pytest)
   - Added trap EXIT to always show diagnostics
   - Added immediate process checks after pytest finishes
   - Added sub-shell execution with immediate cleanup

2. Fixed Subprocess PIPE Blocking:
   - Changed Colab mode from PIPE to DEVNULL to prevent blocking
   - PIPE without reading can cause parent process to wait indefinitely

3. Pytest Session Hooks:
   - Added pytest_sessionstart to log initial state
   - Added pytest_sessionfinish for aggressive cleanup before exit
   - Shows all child processes and their status

This should reveal exactly where the hang is happening.

packages/leann-core/src/leann/embedding_server_manager.py

@@ -402,11 +402,12 @@ class EmbeddingServerManager:
         """Launch the server process with Colab-specific settings."""
         logger.info(f"Colab Command: {' '.join(command)}")
 
-        # In Colab, we need to be more careful about process management
+        # In Colab, redirect to DEVNULL to avoid pipe blocking
+        # PIPE without reading can cause hangs
         self.server_process = subprocess.Popen(
             command,
-            stdout=subprocess.PIPE,
-            stderr=subprocess.PIPE,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
             text=True,
         )
         self.server_port = port